RESONANT DEGENERATE 4-WAVE-MIXING DETECTION OF HCO

The HCO radical has been detected by degenerate four wave mixing D4WM) spectroscopy following 308 nm photolysis of CH3CHO. Spectra have been obtained for the (0, 11, 0) <-- (0, 0, 0) and (0, 10, 0) <-- (0, 0, 0) vibronic transitions of the A2A'' <-- X2A' band system, and the effects of Renner-Teller rovibronic coupling to the dissociative X state have been investigated. The most important observation is the enhanced spectral resolution that is obtained in D4WM spectroscopy, which results from the Lorentzian cubed line profile that is predicted for degenerate four wave mixing spectroscopy in the limit of extreme homogeneous broadening (stationary atom limit). We estimate the detection limit to be approximately 1 X 10(12) cm-3 quantum state-1.